1. Field of the Invention
The present invention relates to a valve manifold for controlling fluid flow between a main flowline and a pressure sensor and, more particularly, to such a valve manifold of modular, two-part construction.
2. Description of the Prior Art
It is often desirable to determine the flow or pressure of a fluid, e.g., a gas, through a main flowline, e.g., a pipeline. Typically, this can be accomplished by a flow restriction disposed in the main flowline, there being pressure taps on each side of the restriction for obtaining high and low pressure fluid pressures. Such a flow restriction may comprise an orifice plate, a flow nozzle, a venturi tube, etc. The high and low pressures taken from opposed sides of the flow restriction in the main flowline are detected by a pressure sensor/transmitter assembly that measures and transmits the measured pressures or pressure differential by a suitable mechanical or electronic signal or the like to a remote location, e.g., a control room, where the pressure or pressure differential may be monitored and/or recorded by an operator.
Typically, a valve manifold is mounted between the main flowline and the pressure sensor. The manifold is used to control flow to the pressure sensor while permitting blocking, venting, zero checks, and calibration. The manifold typically includes a plurality of valves, each movable between open and closed positions relative to a flow pathway in the manifold so as to control the flow of fluid through the pathway.
Fluid pressure sensors/transmitters, particularly such sensor/transmitters of the differential pressure type typically employ diaphragms in both the low and high pressure inlets to the pressure sensors to detect the high and low pressures to which they are exposed. One type of pressure transmitter, commonly referred to as the "coplanar transmitter" is disclosed in U.S. Pat. No. 4,466,290 to Frick, herein incorporated by reference. As shown in the Frick patent, the diaphragms have fluid facing sides, the peripheries of which are defined by rims, the planes defined by the rims being coplanar with respect to one another. In any event, the diaphragms, as seen in the Frick patent, are closely adjacent the face of the transducer in which they are disposed.
Diaphragms that are used in sensors transmitters such as the sensor transmitter disclosed in the Frick patent are extremely fragile, expensive, and difficult to install in the pressure sensor. Further, in cases where the valve manifold and the pressure sensor are directly coupled to one another, the diaphragms are closely positioned to the face of the manifold to which the pressure sensor is attached. In these direct coupled manifold/pressure sensor assemblies, one face of the manifold, generally referred to as the instrument face, sealingly abuts a face of the pressure sensor, as, for example, face 53 of transducer 14 shown in the Frick patent. The instrument face of the manifold is provided with a low pressure outlet and a high pressure outlet, both of which are relatively shallow, cylindric cavities. The cylindric cavities are in register with the low pressure and high pressure inlets, respectively, in the face of the pressure sensor sealingly abutted by the instrument face of the manifold. Accordingly, when the manifold and pressure sensor are mated, the cylindric cavities cooperate with the diaphragms to form generally cylindric chambers of a small cylindrical height relative to the cylindrical diameter.
Not infrequently, it is necessary for the transmitter to be repaired, necessitating its removal from the manifold. Obviously, when the transmitter is removed from the manifold, and in the usual case, the diaphragms are exposed and, being of such fragile nature, readily susceptible to damage.
One way of avoiding field damage of the diaphragms is to remove the entire manifold/pressure sensor transmitter assembly from the field. However, this requires an additional means of controlling the process fluids emanating from the orifice plate assembly or the like. Typically, this would involve an additional set of block valves installed in the feed lines from the orifice plate assembly so that flow from the main pipeline can be stopped when the manifold/transmitter assembly is removed.
Although not necessary, it is desirable that the transmitter be mounted vertically, i.e., that the diaphragms be disposed generally horizontally and facing downwardly. Prior art solutions to this problem of orienting the transmitter involve various complex passageway constructions within the manifold that will effectively accomplish a "right-hand turn" of the passageway within the manifold body. Frequently, this requires passageways drilled at various angles, which requires expensive tooling and precise machining. Moreover, these complex passageway systems often require "construction holes," which are simply bores in the manifold body that allow certain passageways to be drilled and connected with other passageways interiorly of the manifold. These construction holes, even though they are later plugged, are a potential source of leakage. Alternately, they frequently provide dead spaces within the manifold body where liquid and gas bubbles can collect. Thus, elimination of the construction holes eliminates one possible source of leakage and liquid collection or pooling in the manifold body.